PROCEDURE DETAILS
ACQUISITION TECHNIQUE
PATIENT POSITION
Patient must be placed in supine position and the lens of the eyes have to be as far as possible out of the radiation area.
The head should be immobilized in a neutral position; for this porpuse, it is useful to adjust the patient's head with pillows to establish the correct position taking into account the reference lines.
The sagittal reference line must be located in the mid-sagittal plane crossing the glabella and gnathion.
The axial reference line must be parallel to the orbitomeatal plane (Figure 9).
Fig. 9: Prior to the acquisition, the patient must be correctly placed in order to obtain a high quality data. The sagittal reference line must be located in the mid-sagittal plane crossing the glabella and gnathion and the axial reference line must be parallel to the orbitomeatal plane.
ACQUISITION TECHNIQUE
Acquisition area must be defined from arcuate eminence to the lower end of the mastoid portion of the temporal bone.
As the temporal bone involve small and complex structures,
the imaging resolution is very important.
Despite a helicoidal technique provides better resolution,
with a thin collimation there is not significant differences between non-helicoidal and helicodal technique.
However,
the non-helicoidal technique allows to perform better reformarts decreasing the susceptibility to motion artifact [Swartz J,
Loevner L.
Imaging of the Temporal Bone.
4th edition.
Thieme.].
STANDARD REFORMATS
Prior to perform the standard and advanced reformarts,
the raw data must be processed.
This is reconstructed individually for each ear into 0.6 mm axial images in bone algorithm at a DFOV of 100 mm.
The raw data are also reconstructed into 1 mm axial images in soft tissue algorithm including both ears and the brain. To perform the standard and advanced reformats,
the 0.6 mm images are brought up on the CT scanner console where the images are displayed in three orthogonal planes.
AXIAL REFORMAT
In order to perform the axial reformat,
the technologist scrolls through the sagittal data to find an image where the anterior and posterior section of the LSC are observed (Figure 10.A).
Then,
a reference line crossing these sections is traced; if this line is correctly established,
the LSC will be entirely displayed in its longitudinal axis (Figure 10.D). A 0.6 mm (image thickness) x 0.5 mm (distance between images) axial dataset is made parallel to such line from the inferior portion of the tympanic membrane (Figures 10.B and 10.E) to the superior portion of the SSC (Figures 10.C and 10.F).
Fig. 10: Making an Axial reformat. In the saggital view, a reference line is traced crossing the anterior and posterior section of the LSC (A) and the structure is entirely observed in its longitudinal axis (D); the axial dataset is made parallel to this line from the inferior portion of the tympanic membrane (B, E) to the superior portion of the SSC (C, F).
If the axial reformat has been performed correctly,
the LSC,
cochlear fossete,
modiolus,
and stapes footplate are clearly observed.
CORONAL REFORMAT
Similar to the method explained above,
the technologist scrolls through the sagittal data until the anterior and posterior section of the LSC are observed and a reference line is drawn crossing both sections (Figure 11.A). A 0.6 mm (image thickness) x 0.5 mm (distance between images) coronal dataset is performed perpendicular to this reference line (Figures 11.A and 11.D) from the anterior portion of the cochlea (Figures 11.B and 11.E) to the posterior portion of the PSC and SSC (Figures 11.C and 11.F).
Fig. 11: Making a Coronal reformat. A reference line is made perpendicular to the reference line used for the axial reformat (A, D). The coronal dataset is then made from the anterior portion of the cochlea (B, E) to the posterior portion of the PSC and SSC (C, F).
When the coronal reformat has been made correctly,
the Prussak's space and the facial nerve canal are clearly delineated.
ADVANCED REFORMATS
PÖSCHL REFORMAT
As above,
the technologist scrolls in the sagittal data until the anterior and posterior section of the LSC is observed; then,
a new axial plane is established by drawing a line crossing both sections.
The technologist scrolls through the new axial dataset until the anterior and posterior section of the SSC is displayed as two dots (Figure 12.A).
A reference line is traced crossing both dots,
and the SSC would be observed enterily in its longitudinal axis (Figure 12.B).
The Pöschl dataset is performed parallel to this reference line from the posterior portion of the PSC (Figure 12.C) to the anteromedial portion of the cochlea (Figure 12.D).
Fig. 12: Making a Pöschl reformat. The technologist scrolls in the axial reformat dataset until the anterior and posterior section of the SCC are displayed as two dots. A reference line is traced crossing both dots (A), and the canal will be entirely observed in its longitudinal axis (B). The Pöschl reformat is then made parallel to the reference line from the posterior portion of the PSC (C) to the anteromedial portion of the cochlea (D).
Pöschl reformat is useful for the assessment of temporal bone pathologies associated with the SSC, vestibular acqueduct and the long axis of the cochlea.
STENVERS REFORMAT
The Stenvers reformat is performed in the same axial dataset used for Pöschl reformat.
The technologist scrolls until the anterior and posterior section of the SSC is displayed as two dots,
and a reference line perpendicular to the long axis of the SSC is drawn.
The long axis of the SCC may be established by tracing a line crossing both dots (Figure 13.A).
If the reference line has been made correctly,
the SSC would be observed in a cross-sectional view (Figure 13.B). The Stenvers reformart is made parallel to this reference line from the posterior portion of the PSC (Figure 13.C) to the anterolateral portion of the cochlea (Figure 13.D).
Fig. 13: Making a Stenvers reformat. The Stenvers reformat is made perpendicular to the reference line traced for the Pöschl reformat (A, B) from the posterior portion of the PSC (C) to the anterolateral portion of the cochlea (D).
The Stenvers reformat is useful in the morphology assessment of the cochlea,
facial nerve and round window.
TYMPANOSQUAMOUS SUTURE REFORMAT
This reformat is performed in the 1 mm axial images in soft tissue algorithm which includes both ears and the brain.
The images are brought up on the CT scanner console where the images are displayed in three orthogonal planes. The technologist scrolls through the axial dataset until right and left petrous portion of the temporal bone are displayed,
and a coronal plane is established crossing them (Figure 14.A).
Fig. 14: Making a Tympanosquamous suture reformat. The technologist scrolls through the 1 mm axial dataset until right and left petrous portion of the temporal bone are displayed, and a coronal plane is established crossing them (A). Then, the technologist scrolls through the new coronal dataset until both EAC are displayed (B).
Then,
the technologist scrolls through the coronal dataset until both EAC are displayed (Figure 14.B).
A reference line is traced parallel to the cartilaginous portion of the EAC of the ear which is going to be assessed (Figure 15.A). Perpendicular to this reference line,
in the sagittal view,
the measurement of the maximum and minimum distances between the tympanic and the squamous portions of the temporal bone are performed (Figures 15.B and 15.C).
Fig. 15: Making a Tympanosquamous suture reformat. In the coronal view, a reference line is traced parallel to the cartilaginous portion of the EAC of the ear which is going to be assessed (A). Perpendicular to this reference line, the measurement of the distances between the tympanic and the squamous portions of the temporal bone are performed (B, C).
This reformat is useful in the clinical assessment of patients diagnosed with attic cholesteatoma where maximum and minimum distances have been reported to be increased compared to healthy subjects [Girons-Bonells J,
Fontes-Carame D,
Fité-Gallego A,
Masuet-Aumatell C,
Maños-Pujol M.
Estudio comparativo mediante tomografía computarizada de la morfología de la sutura timpanoescamosa entre colesteatoma atical y oídos sanos.
Acta Otorrinolaringológica de Espala.
2010.
DOI 10.1016/j.otorri.2009.05.008].
COCHLEAR REFORMAT
In the axial dataset,
a reference line is traced through the longitudinal axis of the basal turn of the cochlea (Figure 16.A) and an oblique plane is established parallel to this line.
If the plane is correctly established,
the cochlea will be displayed entirely (Figure 16.B).
In the oblique plane,
a curved plane is performed through the cochlea (Figures 16.B and 16.C),
and it will be displayed unrolled (Figure 16.D).
Fig. 16: Cochlear reformat.
CLINICAL INDICATIONS
As CT imaging is useful for the characterization of bone involvement,
it allows to evaluate the external auditory canal,
middle ear cavity and mastoid air cells.
For some inflammatory and neoplastic lesions,
contrast material may be given and images processed with soft tissue window settings.
MR imaging generally is better for differentiation between soft tissue and fluid that allows a better visualization of the nerves and enhancement of the small structures.
MR imaging is also sensitive for detection of bone marrow edema,
and ir can demonstrate bone involvement not suspected by CT.
There are particular indications for each study; for example,
in facial paralysis,
if a patient persists for more than 3 weeks with symptoms,
a neoplasm must be suspected and investigation should includes contrast-enhanced MR imaging.
Also,
in cholesteatoma,
MRI is indicated particularly diffusion weighted imaging,
which helps to differentiate a recurrent cholesteatoma from cholesterol granuloma,
granulation tissue,
or scar.
For congenital lesions,
if disorders of the first and second branchial arches are being studied,
CT should be perform,
MR imaging can be used as a complementary study.
On the other hand,
if an inner ear malformation requires characterization,
a MRI should be the study of choice.
In patients who had undergone surgery,
CT is safe and allows depiction of the type of procedure,
prosthesis and electrodes,
its localization and relationships.
Also,
in acute trauma CT is the study of choice.
STRUCTURED REPORT
The report should start with the technical descriptions of the acquisitions and the reformats that are made; we acquire 0.6 mm axial scans of the temporal bone using a high-resolution bone technique.
The scans are reconstructed in the axial,
coronal and sagital planes having the lateral semicircular canal as a reference for right and left sides.
Stenvers and Poschl reformats are also made.
Then,
the clinical information and previous studies should be mentioned.
For each side,
it must be described the presence of a normal,
deformed or absent pinna and the appearance of the external auditory canal and tympanic membrane.
The middle ear cavity,
the ossicles and their articulations and the stapes superstructure have to be also detailed.
A description of the inner ear including the cochlea,
vestibule and semicircular canals as well as the oval and round windows need to be informed.
Finally,
the vestibular and cochlear aqueducts and internal auditory canal are evaluated and described.
We depict the course of the facial nerve,
the carotid canal and the jugular foramen,
especially if there are any variants.
A description of whether the mastoids are well pneumatized and aerated,
and the anatomic structure of the temporomandibular joint are included.
If there is a congenital aural atresia,
we include the Jahrsdoerfer classification and conclude with our impression with key points.
FINDINGS
Between January-2013 and August-2015,
682 temporal bone CT studies were performed.
Out of 682 studies,
248 (36.4%) were normal; 233 (34.2%) had a chronic inflammatory pathology,
123 (52.8%) otomastoiditis,
75 (32.2%) mastoiditis,
29 (12.4%) thickened tympanic membrane; 87 (12.8%) congenital,
49 (56.3%) semicircular canal thinning or dehiscence,
9 (10.3%) high jugular bulb,
9 (10.3%) atresia,
6 (6.9%) otosclerosis; 24 (3.5%) fractures; 23 (3.4%) acute inflammatory; and 10 (1.5%) tumors.
58 (8.5%) studies were performed for postoperative assessment.
Complementary study was requested in 33 (4.8%) cases to confirm diagnosis.
Structured report and reformats were detailed fo each clinical indication.
CLINICAL APPLICATIONS
CHRONIC INFLAMMATORY
In the evaluation of patients diagnosed with a chronic inflammatory pathology of the ear, the goal of the CT imaging is to guide the clinical approach and to evaluate for complications.
In addition to the detailed above,
the radiologist should includes in the report if there is a cholesteatoma, or any complication such as perilymphatic or canals fistulas,
tegmen dehiscence and fallopian canal dehiscence.
The size and status (healthy or diseased) of the mastoid should be described including the additus ad antrum.
The radiologist also hast to evaluate and to describe in the report if the external auditory canal is eroded and if the middle cavity ear is well aerated. Finally, the state of the ossicles should be also reported.
CHRONIC OTOMASTOIDITIS
Case 1: 45 years-old male patient with right chronic otitis and trigeminal neuralgia.
CT findings showed occupation of the middle ear and mastoid air cells,
with sclerotics changes in the walls of the mastoid air cells. Coronal standard reformat shows dehiscence of the tegmen tympani,
retracted tympanic membrane and opacification of the middle cavity (Figure 17). These findings are related to chronic otomastoiditis.
Fig. 17: Chronic otomatoiditis. Coronal standard reformat shows dehiscence of the tegmen tympani (black arrow), retracted tympanic membrane (outlined white arrow) and opacification of the middle cavity (short white arrow).
ACQUIRED CHOLESTEATOMA
Case 1: 24 years-old male patient with clinical suspicion of cholesteatoma.
CT imaging findings showed right chronic otomastoiditis.
Soft tissue lesion within the middle ear including the attic,
with erosion and retraction of the ossicles were also observed (Figures 18.A and 18.B).
These findings may be associated with cholesteatoma.
MR imaging was performed to confirm diagnosis.
MRI findings showed permeability of the external auditory canal with occupation of the right mastoid air cells and middle ear due to inflammatory process.
A restricted area in the right Prusack space is observed in coronal ADC and diffussion MRI images (Figures 18.C and 18.D),
which confirms the diagnosis of cholesteatoma.
Fig. 18: Attic cholesteatoma. Coronal and axial standard reformats CT images shows soft tissue lesion within the middle ear including the attic (black arrows), with erosion and retraction of the ossicles (short white arrows) (A, B). Restriction in the attic is observed in coronal ADC and diffussion MRI that confirms the diagnosis (outlined white arrow) (C, D). Axial CISS MRI images confirms the location of the lesion (white arrow) (E).
POSTSURGICAL EAR
In the assessment of postsurgical ear,
the report should includes the type of surgical procedure,
if a mastoidectomy has been performed,
it should be described if it was simple or radical.
In cases of tympanoplastia, prosthesis type and its location,
the state of the ossicular chain and tympanic membrane should be described.
Case 1: 70 years-old female patient with history of otosclerosis and left stapedectomy.
CT imaging findings showed evidence of postsurgical changes in the ossicles and thickening of the oval window.
A hyperdense object is observed which corresponds to the stapes prosthesis.
Pöschl (Figure 19.A),
coronal and axial standard-reformats (Figures 19.B and 19.C) show the tip of the prosthesis has migrated into the vestibule.
Fig. 19: Stapes prosthesis , wire. Pöschl (A), coronal standard (b), and axial standard (c) reformats show the tip of the prosthesis (white arrows) has migrated into the vestibule.
CONGENITAL
In the interpretation of CT imaging of the temporal bone in patients with congenital abnormalities,
the report should be addressed to describe the extent of the external auditory canal atresia and if it is membranous,
bony or mixed; the thickness of the atresia plate,
the pneumatization of the mastoid,
the middle cranial fossa level,
the temporomandibular joint location,
and the presence or absence of cholesteatoma.
In the evaluation of the ossicular chain,
it should be detailed if there is ossicle fusion describing the incudomallear and incudostapedial joints,
or if the ossicles are fused to the atresia plate.
In addition,
the stapes should be detailed if present,
dysplastic or absent because it may be useful information if a prosthesis placement is required. Size of the oval window and middle ear cavity in all three axis should be included as they may be crucial in the surgical planning.
The inner ear structures and size of the internal auditory canal should also be mentioned in the radiology report.
In patients with clinical symtoms of dizziness,
vertigo or hearing loss; or clinical suspicion of third-window,
the semicircular canals should be evaluated looking for dehiscence or thinning.
Stenvers and Pöschl reformats may be useful for this purpose,
mainly in confusing cases where the SSC is not clearly delineated in the standard reformats.
In the evaluation of the jugular bulb,
the radiologist should describe if it is high,
dehiscent and if there is any pathology associated.
HIGH JUGULAR BULB.
Case 1: 17 years-old female patient with pulsatile tinnitus and hearing loss.
CT imaging findings showed focal outpouching of the jugular bulb extending to the level of the internal auditory canal with bony dehiscence and protrusion into the middle ear cavity (Figure 20).
Fig. 20: High-riding jugular diverticulum, dehiscent. Focal outpouching of the jugular bulb extending to the level of the internal auditory canal with bony dehiscence and protrusion into the middle ear cavity (white arrows).
ATTIC CHOLESTEATOMA (PRIMARY)
Case 1: 41 years-old male patient with clinical suspicion of attic cholestatoma.
CT images show an occupation of the epitympanum and enlargement of the tympanosquamous suture.
In the tympanosquamous suture reformat (Figure 21),
maximum and minimum distances were measured where an increase was observed in the pathologic ear (dA = 0.17 mm and dB = 0.13 mm) compared to the healthy ear (dA = 0.08 mm and dB = 0.06 mm).
Fig. 21: Cholesteatoma attic. Maximun and minimum distances between the tympanic and the squamous portions of the temporal bone are increased in the pathologic ear (B) (dA = 0.17 mm and dB = 0.13 mm) compared to the healthy ear (A) (dA = 0.08 mm and dB = 0.06 mm).
ATRESIA
Case 1: 17 years-old male patient with right aural atresia.
In the CT images the pinna is observed disminished with atresia of the external auditory canal without pneumatisation of the atresic plate.
Non-aerated middle ear with decreased size and occupied with material of soft tissue density. Dysplastic malleus and incus with incudomalleal ankylosis and horizontal oriented incus long process,
which is attached to the atresic plate. Normally shaped stapes.
Incudostapedial articulation cannot be depicted (Figures 22 and 23).
Fig. 22: Atresia. Non-aerated middle ear with decreased size and occupied with material of soft tissue density. Dysplastic malleus and incus with incudomalleal ankylosis and horizontal oriented incus long process, which is attached to the atresic plate.
Fig. 23: Atresia. CT three-dimensional reformations in a patient with unilateral microtia with deformed residual pinna (C) and external auditory canal atresia (D).
SEMICIRCULAR CANAL DEHISCENCE
Case 1: 68 years-old female patient with chronic otomastoiditis and conductive hearing loss.
Coronal standard reformats (Figure 24.A and 24.B) and Pöschl reformat (Figure 24.C) show dehiscence of the superior semicircular canal.
Fig. 24: Superior Semicircular Canal Dehiscence. Coronal standard reformats (A, B) and Pöschl reformat (C) show dehiscence of the SSC.
ENLARGED VESTIBULAR AQUEDUCT
Case 1: 19 years-old female patient diagnosed with conductive hearing loss.
Pöschl reformat shows a dilatation of the left vestibular aqueduct,
which has a diameter of approximately 17 mm (Figure 25).
Fig. 25: Enlarged vestibular aqueduct. Pöschl reformat show a dilatation of the left vestibular aqueduct, which has a diameter of approximately 17 mm.
MONDINI SPECTRUM
Case 1: 13 years-old female patient with right hearing loss.
Coronal CT images show an absence of the modiolus (Figure 26.A) and the vestibule was observed dilated (Figure 26.B ande 26.C).
These findings are suggestive of Incomplete Partition type 1 of the Mondini Spectrum.
Fig. 26: Coronal CT images show an absence of the modiolus (A) and the vestibule was observed dilated (B). These findings are suggestive of Incomplete Partition type 1 of the Mondini Spectrum.
FRACTURE
Case 1: 48 years-old male patient with head trauma and hearing loss.
CT imaging shows a longitudinal fracture of right temporoparietal bone that extends to the mastoid portion longitudinally,
with involvement of the bone walls of the external auditory canal with displacement of fragments into the lumen (short white arrows),
and dislocation of the ossicular chain associated with discontinuity of the stapes (white arrow).
Extension of the fracture line to the sphenoid,
with involvement of the walls of the lacerated foramen,
foramen ovale,
carotid canal (outlined black arrow) and lateral wall of the sphenoid sinus.
There is occupation of mastoid air cells with material of soft tissue density.
Facial nerve and otic capsule are also involved (black arrow) (Figure 27).
Fig. 27: Fracture, head trauma and hearing loss. CT imaging shows a longitudinal fracture of right temporoparietal bone that extends to the mastoid portion longitudinally, with involvement of the bone walls of the external auditory canal with displacement of fragments into the lumen (short white arrows), and dislocation of the ossicular chain associated with discontinuity of the stapes (white arrow). Extension of the fracture line to the sphenoid, with involvement of the walls of the lacerated foramen, foramen ovale, carotid canal (outlined black arrow) and lateral wall of the sphenoid sinus. Facial nerve and otic capsule are also involved (black arrow).
TUMORS
In the assessment of patients with tumors,
CT imaging is useful to evaluate the bone involvement of the external,
middle and inner ear; however, in order to define and to characterize the soft tissue,
brain and dural extension,
contrast-enhanced MRI imaging is the gold standard.
Case 1: 76 years-old female patient with diagnosis of squamous cell carcinoma.
Coronal and axial CT images show a mass with bone erosion which involve external,
middle and inner ear (Figures 28.A and 28.B).
Contrast T1-weighted coronal and T2-weighted axial MRI imaging shows involvement of soft tissue and intracranial extension (Figures 28.C and 28.D).
Fig. 28: Tumors. Coronal and axial CT images show a mass with bone erosion which involves external, middle and inner ear (A, B). Contrast T1-weighted coronal and T2-weighted axial MRI imaging shows involvement of soft tissue and intracranial extension.